I really enjoy playing around in Platinum Arts Sandbox and do believe in their cause.  I could spend hours just playing around and creating models.  It's like the lego of 3D, one can easily erect a tower, mountains, hills, or entire cities in a matter of minutes.

I am somewhat disappointed with RPG Builder 3D so far, but it is still in it's early stages of development.  I believe it will be a great tool once it matures enough. Map creation is very simple, perhaps even very similar to any 2D RPG Builder out there.